1. Field of Invention
The present invention relates to an apparatus for the preparation of multiple pollen samples for cryogenic preservation used in development of a pollen bank for plant-breeding purposes. More specifically, the invention relates to an apparatus that applies a vacuum to multiple storage units in a manner that allows for the controlled reduction of the moisture content of a pollen sample, thereby enabling cryogenic preservation of the pollen sample in a viable state for subsequent use for plant breeding.
2. Background of the Related Art
Plant breeding is one of the oldest recorded accomplishments of mankind. The ability to breed plants is an important mark in man's movement from nomadic life to organized society. Today's food crops are essentially the result of mankind's primitive plant-breeding attempts.
The practice of breeding has progressed to a science. Plant breeding became a science when genetic principles gave predictability to plant breeding. Plant breeding is basically man's conscious selection of genetic material instead of nature's selection of genetic material. The success of modern plant-breeding efforts include, for example, the increased productivity of field crops, the development of insect-resistant crops, and the development of disease-resistant crops. Numerous natural factors, however, create obstacles to plant-breeding efforts. These factors include the length of time necessary for development of a plant to its sexual maturity, the length of time to pollen viability, and the length of time to maturity of the pollen receptor. Presently, pollination can only occur when a plant is sexually mature, pollen is viable, and pollen receptors are available. In the case of inbreeding, the timing of these events does not normally create an obstacle to pollination. In hybrid breeding, however, specifically in plants such as maize, the timing of these events creates substantial obstacles to successful plant breeding. Cross pollination, where the pollen of one plant is used to pollinate a second plant requires precise timing. In other words, to successfully cross pollinate two plants, both plants much reach sexual maturity at the same time, pollen of the first plant must be viable, and the pollen receptors of the second plant must be available. The timing of these events, otherwise known as hitting the nick, comprises the rate limiting step in the cross pollination process. This requires careful timing of the maturity of both of the plants, and places severe limits on the physical proximity of the various plants.
One proposed method of solving these problems consists of developing a system of storing pollen in a viable condition in a pollen bank. This eliminates the need to coordinate the timing of sexual maturity of the two plants, and effectively eliminates the problem of requiring close physical proximity of the two plants. An effective method for the long-term storage of large quantities of viable pollen represents a significant advance in plant-breeding efforts. Furthermore, the long-term storage of viable pollen provides a unique ability to conserve and manipulate genetic resources. The ability to retrieve viable pollen, obtained from an individual plant stored for long periods of time, would provide great flexibility in plant-breeding programs. In today's present environment of plant-breeding research, a pollen storage system provides a method to expand molecular marker assisted breeding and transgenic biotechnology breeding programs by creating a germplasm bank of pollen for fingerprinting genetic material for future use in plant-breeding programs.
Methods for storage of viable pollen have been tested with some positive results. The success of these methods, however, varies dramatically based on the plant type involved. For example, maize traditionally is very desiccation sensitive, and also temperature sensitive. Freezing maize pollen directly, by exposure to liquid nitrogen, will completely destroy pollen viability. Other plant types do not exhibit this trait, however, the sensitivity to this type of treatment in many other plants is simply not known at this time. Research on maize pollen storage has shown some limited success using air flotation when large quantities of pollen are stored. An air flotation method of drying prepares maize pollen for medium to long-term storage. The system is somewhat limited as it does not allow the stored pollen to be readily used in commercial plant-breeding programs. The air flotation dries large quantities of pollen for storage. This stored pollen often exhibits less than acceptable levels of viability when employed. This makes the use of stored pollen on a commercial basis unsatisfactory.
U.S. Pat. No. 5,596,838, issued Jan. 28, 1997 and U.S. Pat. No. 5,689,914, issued Nov. 25, 1997, hereby incorporated by reference, disclose methods and apparatuses which enable the cryogenic preservation of pollen and, in particular, maize pollen. These systems involve apparatuses with only one pollen sample chamber, and which utilize manual control of the pressure within the chamber. Such an approach, while effective on a small scale, does not easily adopt to the preparation and preservation of multiple pollen samples on an automatic basis. Accordingly, a need still exists for the preservation and storage of pollen on a scale large enough to support modem research and commercial plant-breeding programs.